In general, an endoscope or a manipulator that is formed of an elongated insertion part, which is to be inserted into an examinee, and an operating part connected at the base end of the insertion part has a bending section at a distal end portion of the insertion part, and the orientation of the distal end can be changed via a bending movement of the bending section. As a mechanism for bending the bending section, a method in which the base end portion of a wire connected to the bending section is pulled by manually turning a knob provided on the operating part is employed. In recent years, research into automation of this bending mechanism has advanced, and techniques for replacing the existing manual knob operation with a motor-driven one have been actively researched (for example, see PTLs 1 and 2). In general, in motor-driven operation, by rotating a motor by an amount proportional to the operation level input to the operating part, the bending angle of the bending section can be changed by an amount of bending corresponding to the operation level.
However, in practice, due to the friction between the wire and a surrounding member, slack in the wire, or a similar reason, the amount of pull applied to the base end portion of the wire is less likely to be fully transmitted to the distal end of the wire. In other words, the amount of pull on the wire and the amount of bending of the bending section have a nonlinear relationship. Moreover, this nonlinearity varies depending on the bending shape of the insertion part. Hence, good and consistent bending-movement responsiveness of the bending section to an operator's operation cannot be obtained by simply making the amount of rotation of the motor proportional to the operation level.
To counter this problem, in PTLs 1 and 2, focusing on the amount of travel of the wire or the tension in the wire, serving as an indicator of the bending shape of the bending section or main section, which is a cause of the degradation in the bending-movement responsiveness of the bending section, the motor is controlled such that the degradation and variation in the responsiveness of the bending section are compensated for on the basis of the amount of travel of the wire or the tension in the wire, thus improving the responsiveness.
Besides the bending shape of the bending section or main section described above, there are other causes of the degradation in the bending-movement responsiveness of the bending section.